1. Virus-Cell Interaction Section, HIV Drug Resistance Program, National Cancer Institute, Frederick, Maryland 21702-1201
2. Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104
3. Image Analysis Laboratory, Research Technology Program, SAIC-Frederick, National Cancer Institute at Frederick, Frederick, Maryland 21702-1201
4. Panacos Pharmaceuticals Inc., 209 Perry Parkway, Gaithersburg, Maryland 20877